In recent years, in the process of manufacturing semiconductor devices, a process called chemical oxide removal (COR) has been highlighted as an alternative method to dry etching or wet etching for realizing a fine etching process.
A process of etching a silicon oxide film using the COR technique has been known (for example, see Patent Documents 1 and 2). Specifically, in a chamber maintained in a vacuum state, a hydrogen fluoride (HF) gas and an ammonia (NH3) gas are adsorbed onto a silicon oxide film (SiO2 film) on a surface of a semiconductor wafer during the COR process. The gases react with the silicon oxide film to generate ammonium fluorosilicate ((NH4)2SiF6; AFS). The ammonium fluorosilicate is heated and thereby evaporated in the subsequent step so that the silicon oxide film is etched.